I have an mx-850 that won’t communicate. I have 3 other 850s that communicate fine. I have tried 3 rs2-232 remote cables as well at 2 different serial usb adapters. They all work with my 3 good 850s, but no joy connecting to this other remote. I have taken it apart, inspected & cleaned it, but no comm. All self tests pass as usual. I also tried a factory reset. Does anyone have a schematic or fixed this problem before?

Thanx

Mike